1. Field of the Invention
Retroviruses are ubiquitous as pathogens for a wide variety of diseases. The etiology of many cancers are attributed to retroviruses. With the advent of molecular biological techniques, there has been increasing information about the manner in which retroviruses infect, replicate, and cause various disease states. Retroviruses are considered the causal agents of a wide variety of lymphocyte diseases, such as leukemias, lymphomas and T-lymphotropic diseases.
The retroviruses have a basic genetic structure, where the retrovirus has the genes referred to as gag, pol, and env, with frequently one or more additional open reading frames. For a variety of reasons, the retroviruses have proven to be less tractable than other viruses in providing for attentuated strains by passaging of the viruses. The retroviruses tend to be highly infectious and when mutations or lesions occur, two defective viral strains having different mutations may recombine to provide for a newly infectious virus.
There is a substantial interest in being able to provide for vaccines which would provide protection to a host susceptible to infection by the retrovirus. Some consideration has been given to using either individual viral proteins, combinations thereof, or fragments of such proteins or combinations thereof as immunogens. These approaches have only been recently initiated and it is still too early to say if they will provide for a satisfactory solution. In any event, these approaches do not provide the envelope or capsid in its native form, so it is not clear that a strong immune response will be obtained to the viral proteins in their native conformation. There is, therefore, substantial interest in developing vaccines which closely mimic the immunogenicity of the native virus, and have an insignificant probability of reverting to an infectious state.
2. Brief Description of the Relevant Literature
Armstrong, Applied Microbiology (1971) 21:723-725; DeStefano et al, J. Infect. Dis. (1982) 146:451-455; Montagnier et al. 1984, n: Human T-cell Leukemia-Lymphoma Viruses. Gallo, Essex and Gross (editors), Cold Springs Harbor, N.Y., 363-379, report the formation of an atypical interferon in people with systemic lupus erythematosus and acquired immune deficiency syndrome (AIDS). Yamamoto et al, Vet Immun. Immunopath. (1986) 11:1-19 report a feline retrovirus induced T-lymphoblastoid cell-line that produced an atypical alpha-type of interferon.